bluetooth: Generate random service uuid and generate random fake adapter.

This patch includes two changes:
 1. Randomly generate a Service UUID, weighting services from the
    fake devices more heavily.
 2. Randomly pick a fake adapter to use.

Also adds a testing/clusterfuzz/fuzzers/common directory that includes modules
that are useful for other python fuzzers.

BUG=570049

Review-Url: https://codereview.chromium.org/2166913002
Cr-Commit-Position: refs/heads/master@{#407870}
14 files changed